The time-out interval, in milliseconds. If a nonzero value is specified, the function waits until the object is signaled or the interval elapses. If dwMilliseconds is zero, the function does not enter a wait state if the object is not signaled; it always returns immediately. If dwMilliseconds is INFINITE, the function will return only when the object is signaled.

Note The dwMilliseconds value does not include time spent in low-power states. For example, the timeout will not keep counting down while the computer is asleep.

Return value

If the function succeeds, the return value indicates the event that caused the function to return. It can be one of the following values.

Return code/value

Description

WAIT_ABANDONED

0x00000080L

The specified object is a mutex object that was not released by the thread that owned the mutex object before the owning thread terminated. Ownership of the mutex object is granted to the calling thread and the mutex state is set to nonsignaled.

If the mutex was protecting persistent state information, you should check it for consistency.

WAIT_OBJECT_0

0x00000000L

The state of the specified object is signaled.

WAIT_TIMEOUT

0x00000102L

The time-out interval elapsed, and the object's state is nonsignaled.

WAIT_FAILED

(DWORD)0xFFFFFFFF

The function has failed. To get extended error information, call
GetLastError.

Remarks

The
WaitForSingleObject function checks the current state of the specified object. If the object's state is nonsignaled, the calling thread enters the wait state until the object is signaled or the time-out interval elapses.

The function modifies the state of some types of synchronization objects. Modification occurs only for the object whose signaled state caused the function to return. For example, the count of a semaphore object is decreased by one.

The
WaitForSingleObject function can wait for the following objects:

Change notification

Console input

Event

Memory resource notification

Mutex

Process

Semaphore

Thread

Waitable timer

Use caution when calling the wait functions and code that directly or indirectly creates windows. If a thread creates any windows, it must process messages. Message broadcasts are sent to all windows in the system. A thread that uses a wait function with no time-out interval may cause the system to become deadlocked. Two examples of code that indirectly creates windows are DDE and the CoInitialize function. Therefore, if you have a thread that creates windows, use
MsgWaitForMultipleObjects or
MsgWaitForMultipleObjectsEx, rather than
WaitForSingleObject.